The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for controlling the system of the vehicle by determining a surface profile of the road on which the vehicle is traveling.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle rollover control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
There are two types of vehicle attitudes needed to be distinguished. One is the so-called global attitude, which is sensed by the angular rate sensors. The other is the relative attitude, which measures the relative angular positions of the vehicle with respect to the road surface on which the vehicle is driven. The global attitude of the vehicle is relative to an earth frame (or called the inertia frame), sea level, or a flat road. It can be directly related to the three angular rate gyro sensors. While the relative attitude of the vehicle measures the relative angular positions of the vehicle with respect to the road surface, which are always of various terrains. Unlike the global attitude, there are no gyro-type sensors which can be directly related to the relative attitude. A reasonable estimate is that a successful relative attitude sensing system utilize both the gyro-type sensors (when the road becomes flat, the relative attitude sensing system recovers the global attitude) and some other sensor signals.
One reason to distinguish relative and global attitude is due to the fact that vehicles are usually driven on a 3-dimensional road surface of different terrains, not always on a flat road surface. Driving on a road surface with a large road bank does increase the rollover tendency, i.e., a large output from the global attitude sensing system might well imply an uncontrollable rollover event regardless of the flat road driving and the 3-D road driving. However driving on a three-dimensional road with moderate road bank angle, the global attitude may not be able to provide enough fidelity for a rollover event to be distinguished. Vehicular rollover happens when one side of the vehicle is lifted from the road surface with a long duration of time without returning back. If a vehicle is driven on a banked road, the global attitude sensing system will pick up certain attitude information even when the vehicle does not experience any wheel lifting (four wheels are always contacting the road surface). Hence a measure of the relative angular positions of the vehicle with respect to the portion of the road surface on which the vehicle is driven provides more fidelity than global attitude to sense the rollover event when the vehicle is driven on a road with a moderate bank angle. Therefore it is important to identify road bank condition for proper vehicle rollover stability control.
Another example of detecting road profile could be used in powertrain controls, where the control of the air and fuel combination ratio or fuel ignition timing is such that they match the intention of a driver so as for the driving power or driving speed of the vehicle to match the present driving condition. Although the driver can identify the profile of a driving road and to control the vehicle accordingly, the road condition information has not been directly fed back to powertrain controls, since there is no road condition information detected and used for current vehicle control systems. Hence optimum fuel economy may not be achieved.
U.S. Pat. No. 5,703,776 considers using a gear position sensing member of a transmission, an engine revolution sensing member, a loading degree sensing, a brake pedal operating state sensing to provide a very crude measure of the longitudinal slope of the road surface. This invention provides a much more refined estimation of the road slope using the sensor sets equipped with vehicle dynamics control systems.
In another example, an active roll control system using anti-roll-bar does not respond suitably to the side bank in conventional setting, since the presence of road side bank cannot be detected and the system therefore responds to a side bank as if the vehicle were cornering. This can result in unnecessary power consumption for the active anti-roll-bar system. In order to eliminate this, WO 99/64262 provides a very crude estimation of the road side bank using lateral acceleration sensor and vehicle reference speed.
In a further example, a vehicle driven on a road with a sharp side bank may cause false activation for the yaw stability control system and/or roll stability control system due to the fact that large lateral motion is determined through sensor signals even if the vehicle is driven in steady state condition on the banked road.
Therefore, it is desirable in vehicle dynamics control and future powertrain control and vehicle controls to detect accurately the road side bank and the road longitudinal slope or pitch and to properly activate the vehicle control systems.
The present invention provides a system for determining the flatness of a road on which the vehicle is traveling. In one aspect of the invention, a control system for an automotive vehicle having a vehicle body has a roll angular rate sensor generating a roll angular rate signal corresponding to an roll angular motion of the vehicle body, a yaw angular rate sensor generating a yaw rate signal corresponding to a yaw motion of the vehicle body, a lateral acceleration sensor generating a lateral acceleration signal corresponding to a lateral acceleration of a center of gravity of the vehicle body, a longitudinal acceleration sensor generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the center of gravity of the vehicle body, a wheel speed sensor generating a wheel speed signal corresponding to a wheel speed of the vehicle. A controller is coupled to the roll angular rate sensor, the yaw angular rate sensor, the lateral acceleration sensor, the longitudinal acceleration sensor, and the wheel speed sensor. The controller determines a relative pitch angle and a relative roll angle as a function of the lateral acceleration signal, the longitudinal acceleration signal and the roll rate signal. The controller determines a first flatness index as a function of the roll angular rate signal, the yaw angular rate signal, the relative roll angle and a relative pitch angle. The controller determines a steady state pitch angle as a function of the vehicle speed and the longitudinal acceleration. The controller also determines a steady state roll angle as a function of lateral acceleration, vehicle speed and yaw rate. The controller determines a second flatness index as a function of the steady state pitch angle, the relative pitch angle, the yaw rate, the steady state roll angle and a relative roll angle.
In a further aspect of the invention, a method of controlling an automotive vehicle comprises estimating a first flatness index indicative of road flatness, estimating a second flatness index indicative of road flatness, determining a pitch slope in response to the first flatness index and the second flatness index, and determining a bank angle in response to the first flatness index and the second flatness index.
One advantage of the invention is that one angular rate sensor such as a pitch rate sensor may be eliminated.